it cost me $230.00 to get the single certificate in Edmonton
It cost about the same here in Ontario but including a Chinese translation.
Lucky, you're going out of Beijing instead of Hong Kong. In my case, our HK application
only took 6 months to process largely because I lived with my wife in China during the application process. Plus, I mailed them lots of photos every month. They were probably sick of seeing my mail ... LOL.
Regarding her medical, I would do it only after you two complete your application form. Getting all her hukou, police certificate etc etc takes time.
All The Best but don't rush into marriage. Make sure there's a chemistry bond, something you can't determine over the Internet or letters.